Palladium acetate Subject

When furan or substituted furans were subjected to the classic oxidative coupling conditions [Pd(OAc)2 in refluxing HOAc], 2,2 -bifuran was the major product, whereas 2,3 -bifuran was a minor product [12,13]. Similar results were observed for the arylation of furans using Pd(OAc)2 [14]. The oxidative couplings of furan or benzo[i]furan with olefins also suffered from inefficiency [15]. These reactions consume at least one equivalent of palladium acetate, and therefore have limited synthetic utility. 

By Intramolecular Heck Coupling. l-Bromo-1,5-dienes and 2-bromo-1,6-dienes cyclize in the presence of piperidine and a palladium acetate-tri-o-tolylphosphine catalyst to produce cy-clopentene derivatives (eq 39). 2-Bromo-l,7-octadiene, when subjected to the same reaction conditions, cyclized to yield a mixture of six and five-membered ring products, whereas competing dimerization and polymerization was observed for the more reactive 2-bromo-1,5 dienes. 

The protection of the hemiacetal hydroxyl in step C is followed by a purification of the dominant stereoisomer. The C-6 methyl group is introduced in step C by conjugate addition of dimethylcuprate. The enolate is trapped as the silyl enol ether and oxidized to the enone by palladium acetate. The enone from step D is then subjected to a Wittig reaction. As in several of the other syntheses, the hydrogenation in step E is used to establish the configuration at C-4 and C-6. 

To palladium acetate (1.8 mg, 7.8 //mol) placed in a Schlenk-type tube under a nitrogen atmosphere is added 1,1,3,3-tetramethylbutyl isocyanide (16.8 mg, 0.12 mmol) under stirring at rt. >eep red color is observed immediately, indicating the formation of active palladium(0)-isonitrile catalyst. To the mixture successively added at rt are toluene (0.1 mL), (dimethylphenylsilyl)(pinacolato)borane (102 mg, 0.39 mmol), and 3-(/er/-butyldimethylsilyloxy)-l-propyne (91 mg, 0.53 mmol). The resulting mixture is heated to reflux for 1-4 h, then cooled down to rt, and finally subjected to a short column chromatography on silica gel (diethyl ether) to remove the catalyst. Further purification by bulb-to-bulb distillation of the crude product gives the title compound in 83% 3deld. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Nucleophilic Substitution of xi-Allyl Palladium Complexes. TT-Allyl palladium species are subject to a number of useful reactions that result in allylation of nucleophiles.114 The reaction can be applied to carbon-carbon bond formation using relatively stable carbanions, such as those derived from malonate esters and (3-sulfonyl esters.115 The TT-allyl complexes are usually generated in situ by reaction of an allylic acetate with a catalytic amount of fefrafcz s-(triphenylphosphine)palladium... 

The 1,3-diene moiety in 227 which included the carbon atoms and CVC was oxidized to the l,4-dihydroxy-2-ene moiety in 238 that was further exploited to functionalise the A-ring as well as for the annulation of the C-ring (Scheme 37). The transformation of 227 into 238 was realized by a diastereoselective epoxidation of 227 to afford a vinyl epoxide (241) that was subjected to the conditions for a Palladium(O)-catalysed allylic substitution with the acetate ion [126]. The mechanism and the stereochemical course of the allylic substitution may be explained as depicted in Scheme 37. Sn2 ring opening of the protonated vinyl epoxide 241 by an anionic Pd complex proceeded with a (3Si) topicity to the r-allyl Pd com-... 

The second coupling component, 6-aminocarbazole 1082, was prepared starting from the same known O-tosylate 1063 (165,665). Thus, Buchwald-Hartwig palladium-catalyzed amination of 4-bromonitrobenzene (1076) with 1063 afforded the diaryla-mine 1077. Treatment of 1077 with an excess of Pd(OAc)2 in acetic acid led to the carbazole 1078 in 53% yield. After protection of the carbazole nitrogen with a 2-trimethylsilylethoxymethyl (SEM) group, the product 1079 was subjected to alkaline... 

V-(9-Fluorenylmethoxycarbonyl)-0-(2,3,4-tri-0-benzoyl- 3-D-xylopyranosyl)-L-serine 15. The Fmoc O-xylosyl serine benzyl ester 13 (1.0 g, 1.2 mmol) is stirred in methanol (40 mL) at room temperature and subjected to hydrogenolysis for 18 h under atmospheric pressure using palladium-charcoal (0.2 g, 5%) as the catalyst. The educt 13 dissolves slowly. The catalyst is filtered off, and the solvent evaporated in vacuo. If the residue is not pure according to thin-layer chromatography (TLC), it is dissolved in 2 mL of ethyl acetate and purified by chromatography on a short column of silia gel 60. The byproducts are eluted with petroleum ether-ethyl acetate the product 15 with methanol yield 0.85 (92%) mp 109°C, [cr]D -12.6° (c 0.3, CH3OH) Rf 0.64 (toluene-ethanol, 1 2). 

First discovered by Moiseev et a/.,416 the palladium-catalyzed acetoxylation of ethylene to vinyl acetate has been the subject of very active investigations, particularly in industry, as shown by the considerable number of patents existing in this area. Vinyl acetate is an extremely important petrochemical product which is used for the synthesis of polymers such as poly(vinyl acetate) and poly(vinyl alcohol). Most of its annual production ( 2.6 Mt) results from the acetoxylation of ethylene (equation 160). 

To a solution of 2-iodo-5-(4-fluorophenylmethyl)thiophene (5.30 g, 16.6 mmol), in anhydrous DMF (5.0 ml) was added (R)-N-hydroxy-N-(3-butyn-2-yl)urea (2.12 g, 16.6 mmol), triphenylphosphine (84.0 mg, 0.32 mmol), bis(acetonitrile)palladium(II) chloride (40.0 mg, 0.16 mmol), copper(I) iodide (16.0 mg, 0.08 mmol), and diethylamine (5.6 ml). The mixture was stirred under nitrogen at room temperature for 22 h and concentrated in vacuum at 32°C. The residue was subjected to chromatography on silica eluting with 2-7% MeOH in CH2CI2, crystallization from ethyl acetate-hexane and trituration in CH2CI2 to afford (R)-N- 3-[5-(4-fluorophenylmethyl)thien-2-yl]-l-methyl-2-propynylVN-hydroxyurea as a cream-colored solid 0.94 g (18%), melting point 135°-136°C, (dec). 

The residue was subjected to azeotropic operation with toluene two times, and ether was added to the residue. The precipitate derived from trioxane was removed by filtration and washed with ether, and the combined ethereal solutions were concentrated under reduced pressure. The residue was dissolved in ethyl acetate, and the solution was washed with water and aqueous saturated solution of sodium chloride, was dried, and was concentrated to give 4 g of an oily material. The oily material was dissolved in 20 ml of methanol and to the solution was added 20 ml of aqueous 1 N solution of sodium hydroxide, and the mixture was stirred for 14 hours at room temperature. After removal of methanol under reduced pressure, water was added to the mixture, and this solution was acidified to pH 3 with aqueous 2 N hydrochloric acid. The mixture was extracted five times with ethyl acetate, and the ethyl acetate extract was dried and concentrated to give 3.5 g of crude crystals. After addition of ethanol to the crude crystals, the crude crystals were filtered. The filtrate was concentrated, and to the residue was added ethanol and ethyl acetate, and precipitate was collected by filtration. The combined amount of the crude crystals was 1.6 g. After the combined crude crystals were methylated with diazomethane, the reaction product was dissolved in 20 ml of ethyl acetate. To this solution was added 1.5 g of sodium acetate and 300 mg of 10% palladium-carbon, and the mixture was stirred for 2 hours under hydrogen. Then, the reaction product was filtered, and after addition of aqueous saturated solution of sodium hydrogen carbonate to the filtrate, the mixture was extracted two times with ethyl acetate. The extract was washed with an aqueous saturated solution of sodium chloride, dried, and concentrated to give 1.3 g of crude crystals. The crude crystals were recrystallized from ethyl acetate to yield 765 mg of the title compound (melting point 134-135°C, yield 43%). 

The compound of formula (5) is next subjected to selective hydrogenation to convert the acetylenic bond to an ethylenic bond. This can be readily accomplished by a number of different catalysts, such as a nickel catalyst prepared from a nickel salt and NaBFi4, Lindlar catalyst, or 5% palladium on barium sulfate in the presence of qunioline. The reaction was run at one atmosphere. Analyses by nuclear magnetic resonance and vapor phase chromatography showed the correct structure in good quantity. The product obtained was 3,7,ll,15-tetramethylhexadeca-2,5-dien-l-acetate (6), a C2o dienolacetate. 

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